Why buy a diesel-equipped A7? Two words: Torque and economy

Originally published: November 25, 2013

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At first glance, the union of Audi‘s sporty A7 and the company’s 3.0-litre TDI turbodiesel would seem a little unnatural, their marriage a classic case of opposites trying to attract.

The A7 is the swoopiest of Audi’s sedans, its coupe-like lines promising vigorous motoring that may not be quite on par with a real coupe but is at least ahead of a traditional boxy sedan. Diesel engines, on the other hand, are frugal to the point of parsimony but hardly renowned (at least here in Canada) for their sportiness. Long-distance marathoning — not full-throttle sprinting — is their forte, so the mating of the two seems, well, as confounding as a four-eyed actuary wearing socks with sandals getting frisky with a glamorous starlet.

That would be your initial impression, especially if you’ve been brought up with the ill-informed notion that diesels, smoky oil-burners all, are best suited to long-distance trucking and the occasional pickup owner seeking to boast his testosterone level. Diesels are, by their very nature, tougher to civilize and, like Yours Truly, have trouble keeping quiet in polite company.

Unless, of course, you’re talking about one of the recent spate of German-engineered turbodiesels gradually working their way through upper-end car lineups. Long a mainstay of European motoring, diesels are starting to infiltrate North American lineups. Having started in various luxury manufacturers’ SUVs, these turbodiesels are now propagating into more and more sedans. The reason for the proliferation is simple. Various organizations — notably the American National Highway Traffic Safety Administration — are setting ambitious corporate average fleet fuel economy mandates and few powertrains are better at generating the required numbers than a high-compression diesel mated to a turbocharger.

Diesel-powered or no, the A7 is still the sexiest four-door sedan in the segment and possessed of yet another of Audi’s hedonistically luxurious interiors.Handout, Audi

Of course, that’s their motivation. As to why you might want to shop Audi’s TDI-powered A7 instead of its more traditional supercharged, gasoline-fueled V6, that comes down to torque. Peruse the A7’s spec sheet and, if you’re like most horsepower-obsessed North Americans, the base 3.0L gas engine looks mighty attractive. It’s good for 310 horsepower, a more than adequate amount for a mid-sized, mid-priced luxury sedan. It’s certainly more than the 240 hp the A7 TDI produces.

A little further down that same column, however, are the torque figures, and in the turbodiesel’s case it’s outsized: 428 pound-feet to be exact. The gasoline-powered V6 of the same displacement can only manage 325 lb.-ft. despite its supercharging. Now, most people don’t understand much about torque other than the fact that, like horsepower, more is better. But, unlike horsepower, which thrives on revs, the lower down the rpm range the torque peak occurs, the more immediate the throttle response.

The diesel A7 pumps out 428 pound-feet of torque at a low rpm.Handout, Audi

In the Audi’s case, that 428 lb.-ft. of boosting force occurs as low as 1,750 rpm. That means, when the gasoline engine is barely clearing its head from the lethargy of idling, the 3.0L TDI is at the ready. The effect can be startling.

If, for instance, you were applying long blasts of full-throttle (which I, of course, only do when I am testing said cars in their German homeland; wink, wink donchaknow), the gas engine’s revability — there’s 2,000 rpm more to be had at the top of the rev range — would obviously prove superior. There is, as the engine tuner’s dictum states, no substitute for revs.

But here in the world of Draconian speed limits, “punch” matters more than outright speed. Unable to sustain long full-throttle blasts, we North Americans instead look for jump off the line and instantaneous passing, both attributes, especially the latter, the A7 TDI possesses in spades. Its 5.7-second zero to 100 kilometres an hour time — barely 0.1 seconds slower than the gasoline engine — belies any inherent disadvantage you might have attributed to diesel propulsion. And the big A7 easily lunges past long trucks, with the diesel’s turbocharger on the boil and the eight-speed automatic always at the ready. Anyone thinking there’s a huge performance penalty for the diesel burner’s promised parsimony just hasn’t driven a diesel lately.

Indeed, the A7 TDI does prove frugal. At a steady 120 km/h, it’s easy to achieve 6.7 L/100 km. Bump it up to 130 klicks and the Audi’s digital fuel economy readout barely notices, the average creeping up to just 7.1 L/100 km. Around town, the diesel isn’t quite as impressive, averaging about 11 L/100 km. Factor in typical usage of 55% city and 45% highway, and you’ll probably average about the 9 L/l00 km I did in two weeks behind the wheel. That’s about the same as a Ford Fiesta ST and its 1.6L Ecoboosted four.

And, as I mentioned, the penalty for all this stinginess is minimal. Other than the relative scarcity of diesel pumping stations, there’s but a hint of the high-compression/high fuel-pressure clatter endemic to diesels. At anything over idle, it disappears. Almost everyone who rode in this particular A7 had no idea it was diesel-powered, including a few autojournalists familiar with the Audi.

Indeed, other than the $2,500 premium Audi Canada demands for the diesel engine in the A7, there’s precious little reason not to buy one. Diesel-powered or no, the A7 is still the sexiest four-door sedan in the segment and possessed of yet another of Audi’s hedonistically luxurious interiors. Only, in this case, its fuel gauge doesn’t plummet quite as fast towards E.